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Ministry of Defence

INTERIM

Defence Standard

00-25 (PART 5) / ISSUE 1 29 M a y 1 9 9 2

HUMAN FACTORS

FOR DESIGNERS OF EQUIPMENT

PART 5: STRESSES AND HAZARDS

DSTAN

Please see last pages for details of latest Amendment Action

INT DEF STAN 00-25 (PART 5)/1

AMENDMENTS ISSUED SINCE PUBLICATION

AMD NO DATE OF TEXT AFFECTED SIGNATURE &ISSUE DATE

Revision Note

Historical Record

Arrangement of Defence Standard 00-25

Human Factors for Designers of EquipmentPart 1 - IntroductionPart 2 - Body SizePart 3 - Body Strength and StaminaPart 4 - Workplace DesignPart 5 - Stresses and HazardsPart 6 - Vision and LightingPart 7 - Visual DisplaysPart 8 - Auditory InformationPart 9 - Voice CommunicationPart 10 - ControlsPart 11 - Design for MaintainabilityPart 12 - SystemsPart 13 - Human Computer Interface Design Guidelines

Two or more Parts may apply to any one equipment and it is thereforeessential that all Parts be read and used where appropriate.


HUMAN FACTORS FOR DESIGNERS OF EQUIPMENT


PREFACE

i This Part of the Defence Standard takes into account some of the mainenvironmental factors which affect work efficiency and personnelwell-being. These should be considered by designers in defence equipmentapplications.

ii This Part of the Defence Standard is published under the authority ofthe Human Factors Subcommittee of the Defence Engineering EquipmentStandardization Committee (DEESC).

iii This Standard should be viewed as a permissive guideline, rather thanas a mandatory piece of technological law. Where safety and health isconcerned, particular attention is drawn to this Standard as a source ofadvice on safe working limits, stresses and hazards etc. Use of thisStandard in no way absolves either the supplier or the user from statutoryobligations relating to health and safety at any stage of manufacture oruse.

iv Users of this Standard shall note that some material may be claimed tobe subject to copyright in this or other countries. Copyright where knownis acknowledged.

v This Standard has been devised for the use of the Crown and itscontractors in the execution of contracts for the Crown. The Crown herebyexcludes all liability (other than liability for death or personal injury)whatsoever and howsoever arising (including, but without limitation,negligence on the part of the Crown its servants or agents) for any loss ordamage however caused where the Standard is used for any other purpose.

vi This Standard has been agreed by the authorities concerned with its useand shall be incorporated whenever relevant in all future designs,contracts, orders etc and whenever practicable by amendment to thosealready in existence. If any difficulty arises which prevents applicationof the Defence Standard, the Directorate of Standardization shall beinformed so that a remedy may be sought.

vii Any enquiries regarding this Standard in relation to an invitation totender or a contract in which it is incorporated, are to be addressed tothe responsible technical or supervising authority named in the invitationto tender or contract.

viii This Part of the Defence Standard is being issued as an INTERIMStandard. It shall be applied to obtain information and experience of itsapplication. This will then permit the submission of observations andcomments from users using DGDQA Form No 0825 enclosed.

A review of this INTERIM Standard should be carried out within 12 months ofpublication. Based on the comments received the author and/or thecommittee responsible for the preparation of the Defence Standard shalljudge whether the INTERIM Standard can be converted to a normal Standard ordecide on what other action should be taken.

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PAGE

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CONTENTS

Preface

Section One. General

0 Introduction1 Scope2 Related Documents3 Definitions

5556

Section Two. Submarine Atmosphere

778

4 Introduction5 Control6 Maximum Permissible Concentrations (MPCs)

Section Three. Acceleration and Deceleration

97 Acceleration

Section Four. Wind

168 General

Section Five. Motion

9 Whole Body Motion Phenomena 17

Section Six. Vibration and Shock

2110 Vibration

Section Seven. Weightlessness

11 General 23

Section Eight. Effects of Noise

12 General 26

Section Nine. Darkness and Dazzle

3013 General

Section Ten. Effects of Radiation

14 Ionizing Radiation 31

Section Eleven. Chemical and Biological Contaminants

15 General 34

Section Twelve. Safety Standards

16 Guidelines 36

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CONTENTS (Contd)

Section Thirteen Thermal Environment

17 General

PAGE

37

Section Fourteen Combined Environmental Stressors

18 Definition of Terms 41

Section Fifteen Effects of Sleep Loss

19 Introduction 47

Annex AAnnex B

Table 1

Table 2Table 3Table 4

Figure 1

Figure 2

Figure 3

List of Related Documents and PublicationsSources of Advice

Relation Between Sound Level and Duration for anL e q of 85 dB(A)Typical Responses to Effective Temperature (ET)Interpretation of Windchill Index (KO)Stressor Interactions

Dynamic Response to a Triangular Acceleration PulseDepending Upon the Ratio of Pulse Length (t) to theNatural Period of the SystemHuman Tolerance to ±Gx and ±Gy Impacts Under VariousConditions of Body RestraintHuman Tolerance to ±Gx and ±Gz Impacts Under VariousConditions of Body Restrains

A-1B-1

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373943

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13

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HUMAN FACTORS FOR DESIGNERS OF EQUIPMENT


Section One. General

0 Introduction

There is an optimum environment in which man works most effectively.Changes from this optimum, if sufficiently large, result in adverseeffects. These may appear as discomfort, degradation in job performance,physiological changes or ill-health.

Performance limits will normally lie between comfort and physiologicalcriteria. However, in some circumstances discomfort will itself result inperformance decrement and thus to preserve performance the stricter comfortcriterion is to be employed.

In other circumstances the physiological limit must be employed as someenvironmental substances can have imperceptible effects which will renderan individual incapable of rational perception of changes in his ownbehaviour.

This part of the Standard discusses the environmental factors (collectivelyknown as stressors) which can adversely influence task performance andindividual well-being. It indicates limit values where available andsuggests ameliorative techniques where stressors exceed appropriate limits.

The information available is not always definitive, and some limits aremerely advisory. For other factors, mandatory limits and procedures apply.

1 Scope

This Part of the Standard considers some of the main environmental factorswhich affect work efficiency and personnel well-being. These should beconsidered by designers in defence equipment applications.

2 Related Documents

2.1 The documents and publications referred to in this Part of the DefenceStandard are listed in annex A.

2.2 Reference in this Part of the Standard to any related documents meansin any invitation to tender or contract the edition and all amendmentscurrent at the date of such tender or contract unless a specific edition isindicated.

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2.3 Related documents can be obtained from:

DOCUMENT SOURCE

British Standards (BS) BSIInternational Standards (ISO) Sales Department

Linford WoodMILTON KEYNES MK14 6LE

Tel: 0908 221166

Defence Standards Directorate of StandardizationKentigern House65 Brown StreetGLASGOW G2 8EX

Tel: 041-224 2531/2

Joint Services Publication (JSP) MOD Forms & Publications BranchMwrwg RoadLlangennechLlanelli SA14 8YP

Tel: 0554 820771 Ext 4058

Book of Reference (BR) Ministry of Defence CS(PS)3Building 25ARoyal Arsenal WestLONDON SE18 6TJ

Tel: 081 854 2044 Ext 2938

3 Definitions

3.1 For the purpose of this Part of the Defence Standard the followingdefinitions apply.

3.2 Hertz (Hz). SI unit of frequency, indicating the number of cycles persecond (c/s).

3.3 L eq. The steady sound level which would produce the same, energy overa stated period as specified time-varying sound. Provided the "Leq" andlong-term r.m.s are equivalent.

3.4 Lux. Unit of illuminance or illumination in the SI system, 1 lumenper square metre.

3.5 Sievert unit. A unit of x-ray dose, being the dose of radiationdelivered in 1 hour at a distance of 10 mm from a point source of 1 mg ofradium element enclosed in platinum 0.5 mm in thickness.

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Section Two. Submarine Atmosphere

4 Introduction

The need for personnel to spend extended periods within the enclosed,sealed environment of a submarine requires special consideration. Withoutaction, atmosphere contaminants and waste products produced either from thepersonnel themselves or from the submarine’s machinery and constructionmaterials will rise to exceed acceptable levels. Oxygen on the other handwill be utilized causing diminishing levels; both trends continuing untilexternal ventilation can take place again.

4.1 The Hazard

4.1.1 Submarine atmospheres contain a complex mixture of agents in gaseousvapours and aerosol form which may pose a number of different hazards:

(a) toxicity: ranging from the acute effects of short exposure to chroniceffects occurring many years after exposure has ceased;

(b) reduction in the performance of personnel such that the performance orsafety of the submarine becomes impaired;

(c) fire and explosion: from the build up of inflammable agents.

4.1.2 The different hazards may in turn be produced by a number ofseparate mechanisms:

(a) the action of a specific contaminant;

(b) interaction of mixtures of contaminants;

(c) specific action of a breakdown product produced by the interaction ofspecific contaminants with the submarine environment;

(d) interaction of mixtures of breakdown products.

5 Control

5.1 The range of both potential hazard and methods of causation identifiesthe need for all materials suggested for submarine use to undergoevaluation before such use is sanctioned. The requirement for acomprehensive evaluation system and the need to maintain levels of certainagents, produce the need for a system of Submarine Atmosphere Control.Such control is exerted by both the passive limitation of quantities ofmaterials allowed on board and by active removal and production systems.

5.2 Passive control. The vast majority of submarine contaminants arecontrolled by a passive system which requires all proposals of material foruse in submarines to be forwarded to Chief Naval Architect, Bath. All suchproposals are evaluated with regard to Toxicity, Fire Characteristics andinterference with atmosphere monitoring systems, following which a decisionis made with regard to the materials suitability and it is listed withinthe Submarine Materials Toxicity Guide: BR1326A.

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5.2 (Contd)

BR1326A thus represents a comprehensive list of all materials that havebeen considered for submarine use, materials not included in the book havenot been evaluated and are not be used. Detailed instructions on theprocedure for clearance of a material and the information required from thesponsor are included in the volume itself and promulgated by DCI. Itshould be noted that evaluation may be time consuming and complex thusclearance may take a significant time. The volume is reissued by CNA every6 months.

5.3 Active control. In addition to the passive control measures containedwithin BR1326A, submarines are equipped with varying systems for activeremoval of certain contaminants and for the production of oxygen. Detailsof the machinery and individual submarine fitments are contained withinBR1326 Air Purification in Submarines.

6 Maximum Permissible Concentrations (MPCs)

6.1 Both active and passive control systems require the promulgation ofsafe levels for some atmospheric agents, to provide design constraints forwhat must be achieved. Within industry safe levels are specified by theAmerican Conference of Governmental Industrial Hygienists as ThresholdLimit Values (TLVs) and by the Health and Safety Executive and OccupationalExposure Limits (OELs). However, both these systems are specified forsingle agents for an eight hour day, 40 hour week, industrial exposure andare thus totally unsuitable for use within submarines. A unique system oflevels is therefore promulgated within BR1326 exclusively for use withinsubmarines as Maximum Permissible Concentrations (MPCs) for a maximum90 days continuous exposure. These levels take into account effects ofbreakdown and mixing as well as constant exposure. This allows theirspecification as ceiling or maximum values unlike most other industrialvalues which are quoted as time weighted averages.

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Section Three. Acceleration and Deceleration

7 Acceleration

7.1 Acceleration occurs whenever there is a change in velocity (linearacceleration), or a change in direction of motion at uniform velocity(centripetal acceleration). The effect of acceleration on man depends upona number of factors including:

(a) Magnitude. Forces due to acceleration are measured in units of G,this being the ratio of the applied acceleration (in metre per sec²) to thestandard acceleration of gravity g, or 9.81 m/s2.

(b) Duration. In their actions on man, accelerations may be broadlyclassified into impact acceleration - those acting for a second or less,and often for only tens of milliseconds, and sustained accelerations -those acting for a second or more. Impact forces are met withinaccidents - vehicle collisions, crashes, ejections etc - and humantolerance is determined by the mechanical strength of the body andirreversible failure of its component bones, ligaments or blood vessels.Sustained accelerations occur during routine flight - particularly inaircraft manoeuvring - and human tolerance depends upon the body’sphysiological response, the limit generally being a reversible loss ofconsciousness. Impact and sustained forces will, therefore, be discussedseparately.

(c) Direction. The vector direction of acceleration forces is definedaccording to a three-coordinate system based upon the long (spinal) axis ofthe body. Note that these axes may differ from those relating to thevehicle, or to the vertical of earth’s gravity, depending upon bodyorientation.

(d) Body restraint. The greater the restraint, the more the body will beaccelerated as a whole and the lower will be forces induced by independentmotion of body parts. Limb and head flailing in a high-speed aircraftejection is an example where injury can be reduced by increased restraint.

(e) Site and area of application. Applying the accelerating force to astrong part of the body (the bony part of the hips, for example) anddistributing it over as large an area as possible will also reduce the riskof producing local injury.

(f) Rate of onset. The body responds to an application of forcedynamically so that the transmitted force may be attenuated, amplified orunchanged depending upon pulse duration or acceleration onset rate.

7.2 In normal circumstances, linear forces tend to be of low magnitude,though carrier operations can expose aircrew to acceleration of ±3Gx forseveral seconds. Much greater and sustained forces are caused by theradial accelerations of aircraft manoeuvring with levels up to +9Gz lastingfor 15 seconds or more.

Impact forces are met within accidents and may exceed 25G in any axis. Thelaunching of free-fall lifeboats or sea survival capsules and the effectsof mines on ships and armoured vehicles are other examples of predominantly+Gz impact forces.

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7.2 (Contd)

Slamming in ships and jolting in land vehicles are more commonplaceexamples of appreciable G forces in both z-and y-axes.

7.3 Tolerance to +G acceleration. With a moderately rapid rate of onsetof acceleration (1.0G per sec or more), loss of peripheral vision occurs at+3-4 Gz, blackout at +4-5 Gz and loss of consciousness at +5-6 Gz. A SlOWrate of G onset (0.1 Gs-1) allows the baroreceptor response to developalong with the increasing stress and these tolerance levels are increasedby about 1G. Since modern fighter aircraft are capable of sustaining +8Gz,or more, a considerable degree of aircrew protection is required to preventvisual symptoms and to preclude loss of consciousness. Two methodscurrently employed are the anti-G suit and positive pressure breathing.

7.4 Other acceleration vectors

7.4.1 +Gx (transverse supine G). Cardiovascular tolerance to all axes oftransverse and lateral inertial forces is high, as the vertical height ofthe body is greatly reduced and the vertical pressure gradient betweenheart and brain, in particular, is abolished. Tolerance is greatest whenthe hips and knee are flexed to 90° and body weight supported on anindividually moulded couch, when +15 Gx may be tolerated for many seconds.Breathing becomes difficult at levels greater than +8 Gx and impossible at+12 Gx, though this problem can be overcome by breathing at positivepressure.

7.4.2 ±Gy (left/right lateral G). The effective symmetry of the bodyabout the sagittal plane means that there is no discernible differencebetween the tWO directions of Gy acceleration. Gy acceleration is becomingof interest to aviation, however, with the advent of lateral flightcontrol, though as the levels are quite low, ±1 Gy maximum, no significantphysiological effects are expected.

7.5 Disorientation in flight

7.5.1 Disorientation induced by linear acceleration. The human bodysenses linear acceleration by means of the otolith organs of the inner earand through pressure receptors in the areas of skin which are in contactwith the seat or the floor. When two accelerations are superimposed thesesensors indicate to the brain the direction and magnitude of the singleresultant acceleration. Because the acceleration due to gravity is theonly sustained acceleration experienced in everyday life, the resultant oftwo sustained accelerations will tend to be perceived as gravity alone andtherefore as indicating the vertical. Thus a sustained acceleration in theline of flight tends to generate an illusion of pitch-up and decelerationan illusion of pitch-down. This illusion is known as the somatogravicillusion.

The somatogravic illusion has a visual counterpart the oculogravicillusion, which consists of an apparent movement of the external visualscene, upwards during forward acceleration and downwards duringdeceleration. This illusion is only evident when the visual scene lacksdetail as, for example, during night flying, when fixed ground lights mayappear to be in motion.

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7.5.1 (Contd)

The somatogravic illusion is regularly experienced when an aircraft is putinto a turn. If the manoeuvre is initiated gently and the correspondingroll of the aircraft occurs at a sub-threshold rate (<2 deg/s) the aircraftwill feel to be straight and level and, apart from instrument information,only external vision will indicate the true aircraft orientation. Loss ofexternal vision during a turn may lead to a form of disorientation known as‘the leans’.

7.5.2 The Leans. This illusion consists of a sensation of the aircraftbeing in a banked attitude when it is in unaccelerated straight and levelflight. The illusion only occurs when there is no clear visual horizon aswhen flying in cloud or at night, but may be so powerful as to cause thepilot to lean in his seat towards what he perceives as the vertical. It israpidly dispelled when clear external vision is regained. Correct aircraftcontrol when a pilot is suffering from the leans, as with other forms ofspatial disorientation, is likely to be assisted by the provision of aclear unambiguous attitude display.

7.5.3 Disorientating effects of angular accelerations. The ability toperceive angular acceleration is almost exclusively mediated by thesemi-circular canals of the inner ear. These structures behave as heavilyoverdamped accelerometers. In consequence, during everyday activities theneural signal relayed to the brain represents the angular velocity of thehead. This neural signal is used to generate angular eye movements of anappropriate velocity to maintain a stable visual lineage of earth fixedtargets (the vestibulo-ocular reflex). In terms of frequency response thesystem behaves as an accurate angular velocity transducer down to about0.05 Hz. Below this frequency there is a progressive reduction in gain andan increasing phase error (lead). Thus in circumstances of longer durationangular acceleration the velocity coded signal from the semi-circularcanals underestimates the true head velocity, and in conditions of constantvelocity angular rotation this signal decays to zero. This results invisual blurring of earth-fixed targets and a reduction in the perceptionsof rotation when visual cues are absent. These conditions are exemplifiedby spinning manoeuvres in aircraft.

7.5.4 For all illusions it is vital that instruments should provide clearand unambiguous information about the true aircraft attitude in order toassist the pilot in re-orientating himself.

7.6 Human tolerance to impact accelerations. The effects of impact forcesmay be classified into primary effects caused by whole body acceleration inthe absence of local forces or body displacements; secondary effects causedby missiles, for example, impacts from other components or contents of thevehicle which have not decelerated to the same extent as the occupant; andtertiary effects caused by body displacement. These include a whole rangeof injuries from head impact to broken limbs, ribs etc and depend to agreat extent on vehicle and seat design and the degree of body restraint.The product of acceleration and the time for which it acts gives velocitychange (or v) and, for brief impacts, this becomes the critical factorwhich determines tolerance (compare with long duration acceleration when itis the acceleration level which is critical). The time-dependent change inresponse of the body to acceleration - from velocity change to accelerationlevel - is similar to that seen in a simple mass-spring system, and is

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7.6 (Contd)

related to the ratio of the length of the acceleration pulse to theundamped natural period of the system. Figure 1 shows that for longduration forces (pulse length/period >10) the response is equal to theinput, while for brief impacts (pulse length/period <0.4) the velocitychange is critical. For intermediate values (pulse length/period 1)dynamic overshoot leads to amplification of the response. This is aparticular problem with the forces induced by operation of aircraftejection seats and has led to the use of the dynamic response index, orDRI, a mathematical model of the subject’s compressible spine, to predictthe risk of spinal injury (see ASCC Air Std 61/1B - Ejection AccelerationLimits).

7.7 Body restraint. The whole body impacts considered above assume thatthe force is applied uniformly so that local injuries are precluded. Eachwith optimum restraint, however, some parts of the body will be stressedmore than others, in particular, lateral forces applied to the head mayexceed ±7 Gy.

Fig 1 Dynamic response to a triangular accelerationdepending upon the ratio of pulse length (t)natural period of the system

pulseto the

In practice, man is usually subjected to impact accelerations in conditionsin which full restraint is impracticable, though in a vehicle crash arearward-facing seat with a lap belt to prevent rebound ejection from theseat offers the nearest compromise. At the other end of the scale comesthe exposure to impact of unrestrained sitting or standing subjects wherebody displacement and tertiary injuries will be inevitable unless theimpact forces are very small. Ship shock is a particular example in whichdeck heave caused by mine blast is most likely to cause head injury andbroken limbs, while injury to the feet or ankles is relatively rare.

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7.8 Tolerance criteria. The pass/fail criteria which are used in aparticular condition of impact depend greatly upon the circumstances. Witha potentially lethal impact, major injuries may be accepted and the passcriterion would simply be survival. In an aircraft crash, however, therisks of fire or drowning make it essential that survivors of the impactshould not be concussed or suffer incapacitating bony injuries, so thecriterion becomes more rigorous. For the services, maintenance ofeffectiveness in combat will be a critical criterion.

7.9 Tolerance levels. Tolerance curves exhibit wide differences dependingupon the degree of restraint and the criterion selected. Differences dueto the direction of applied acceleration will also exist.

(a) Horizontal impacts

Fig 2 Human tolerance to ±Gx and ±Gy impactsunder various conditions of body restraint

It may be seen from fig 2 that the greatest tolerance is obtained when theimpact load is most evenly distributed. This is achieved in -Gx impacts(forward-facing crash deceleration) by the restraint of head, arms and legsin addition to a lap belt, shoulder and upper torso harness; but is simplyachieved in a +Gx impact (rearwards–facing seat) with a lap belt to preventthe subject from rebounding out of the seat. The omission of restraint forhead, legs and arms leads to a significant reduction in tolerance, mainlybecause the head is free to move forwards and its peak resultantacceleration may be considerably greater than that of the body. Using onlya lap belt, tolerance is further reduced owing to the very high local beltloads and risk of injury to abdominal organs as the body 'jack-knifes' overthe belt. Optimal positioning of the belt is important.

Tolerance figures given in fig 2 assume that the resulting body motion willnot bring it into contact with any injurious structures, motion of the headagain being critical. With no restraint at all, primary tolerance to -Gxacceleration depends upon the subject’s ability to maintain posture bymuscular effort. Given some support, such as a steering-wheel and footpedals, the trunk can be kept from moving forward at about -4 Gx.

The data upon which the lower two curves are based come from studies ofpassenger transport systems and the tolerance criterion used was publicacceptability of a system intended for everyday use.

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7.9 (Contd)

Exposure of human subjects to lateral acceleration (±Gy) is less frequentthan exposure in the Gx axis, but occurs on primary impact in vehicles withsideways seating and in secondary impacts following rotation of thecrashing vehicle. It also occurs when vehicles are struck from the side.With full restraint, tolerance should be similar to that in the fore andaft axis, but if the head is not restrained, potentially injurious neckloads occur at quite low levels of acceleration. Voluntary tolerancecurves for lap belt and contoured couch restraints are also given in fig 2.

(b) Vertical impacts. Fig 3 illustrates, in the same way, human toleranceto vertical impact. The upper line is similar to that of fig 2, since theacceleration vector is identical (+Gx). The other lines, however, allrefer to ±Gz forces. The second refers to aircraft ejection accelerationson which quite precise data are available. In particular, the effect ofdynamic response is shown by the curved portion which dips below theplateau G level over the critical pulse duration of about 0.2s.

Pulse duration (t),s

Fig 3 Human tolerance to +Gx and ±GZ impactsunder various conditions of the body restraint

Fewer data is available on unrestrained subjects in whom tolerance dependson leg muscle strength, the crossover of the two lines is due to thegreater energy absorbing capacity of flexed legs (as in jumping).

No attempt has been made to include actual data points nor ranges, infigs 2 and 3. These tolerance curves must, therefore, be treated withcaution and are intended only as an indication of the most probable levelof tolerance which could be expected for each of the various situations.

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7.10 Crashworthiness. Crashworthiness implies that the overall design ofa vehicle is such as to minimize the risk of injury in a crash. Itinvolves the maintenance of workspace integrity with adequate seat strengthand restraint; the avoidance of additional hazards such as post-crash fire,fumes, missiles or sinking etc, and the provision of energy absorbingdevices to attenuate the peak forcesparts of his body most at risk.

Specific example of energy absorbingand panels in automobiles to providecrash and energy absorbing seats for

transmitted to the crew member, or to

devices are the use of crushable beamsa controlled stopping distance in ahelicopters in which the seat is

permitted to stroke vertically at a just tolerable level of +Gzacceleration in order to attenuate any greater peak forces. Objects whichmay be struck by a flailing head or limbs should be adequately padded toprevent local injury, the thickness of padding needed and its crushresistance being readily calculable from the anticipated impact parameters.

7.11 Restraint systems. The function of a restraint system is to transferimpact forces from a vehicle to its occupant in such a manner as tominimize the risk of injury. As restraint harnesses will normally be usedfor long periods in the absence of impact forces they should be easy touse, comfortable and offer the minimum of restriction, while stillfunctioning efficiently when needed. Active systems require theco-operation of the user in fastening buckles and so on, while passivesystems such as airbags operate independently of the occupant.

Further details of aircraft restraint systems are given in AP 8C whilespecifications for automobile restraints are given in BS 3254:specification for seat belt assemblies for motor vehicles and in BS AU 183.Industrial restraints are used to arrest potential falls and are covered byBS 1397: specification for industrial safety belts, harnesses and safetylanyards.

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Section Four. Wind

8 General

8.1 Wind velocities of 10 knots and upwards can deleteriously influencewalking and other activities which must be performed in open air. Gusts of45 knots will blow people over, although higher wind speeds can betolerated by leaning into them (Murakami and Deguchi). Speed of walking isreduced by a factor of four in wind speeds of 40 knots.

8.2 Where walking surface is wetted or greasy, slipping may occur,although it is estimated that toppling equilibrium is likely to be lostbefore slipping occurs for any coefficient of friction exceeding u = 0.6(Lloyd).

8.3 Baggy outer clothing will increase the surface area exposed to windand reduce tolerance to wind forces. Where tasks must regularly beperformed in conditions of wind hazard, windshields or windbreaks should beprovided wherever possible. If this is not possible, personnel must beadequately secured to avoid being blown over, eg from ship’s flight decks.Task equipment should provide handholds and harness securing points. Iflightweight, stabilizing mounts should be fitted.

8.4 Task automation should be considered if it is estimated that, afterall measures are taken, wind is likely to constitute a major hazard.

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Section Five. Motion

9 Whole Body Motion Phenomena

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9.1 The motions of military vehicles and platforms can have adverseeffects on the comfort, well-being and task performance of personnel. Insome circumstances, health and safety may also be hazarded.

The consequential induced body motions and their effects appear as fourprimary phenomena:

(a) Motion sickness: low frequency motion and occurring with both shortand long term exposure.

(b) Motion-induced task interruptions: low frequency, large amplitudemotion, specific short-term events. Abrupt changes in acceleration arefrequently present, eg in slamming, jolting or turbulence.

(c) Motion-induced fatigue: low frequency, large amplitude motion andresulting from long-term exposure.

(d) Vibration: medium to high frequency, with exposure time depending ontolerance to the motion severity. Vibration is considered in section sixof this Part.

9.2 Characteristics of inducing motions. International Standard 2631(Parts 1 and3) and British Standard 6841 provide detailed guidance on anddescription of those motions which specifically affect the human.

9.2.1 Motion sickness. Characteristically, sickness occurs as a result ofexposure to motion in the frequency range 0.05 to 0.7 Hz, while vibrationeffects are primarily seen between 0.5 and 80 Hz.

Motion sickness appears to be predominantly due to linear acceleration inthe vertical (z) axis, although rolling (rotation about the x-axis) andpitching (rotation about the y-axis) may also contribute. Lateral lowfrequency motions may also cause sickness but this is not well-quantified.The peak frequency for incidence is about 0.17 Hz, while incidence alsoincreases steadily with r.m.s acceleration over the range considered.

It should be noted that these data are derived from studies employingsingle sinusoidal applied motions. The effects of complex motions are lesswell known and a variety of models have been developed in an attempt torepresent multiple-frequency effects (see Burns and Smith). However, untilmore data is available, the treatment of the effects of both broadband andmultiple-frequency motion, including significant non-vertical components,remains equivocal.

Over longer periods (3-4 days), adaptation to motion usually occurs and theincidence of sickness declines. Since such habituation is to particularmotions, however, changes in motion characteristics can result in are-occurrence of the illness syndrome.

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9.2.1 (Contd)

Motion sickness incidence should not be used as an unqualified predictor ofthe likely effect on task performance. For experienced personnel,conditions can be such that task performance is affected although symptomsof motion illness are not experienced (McLeod et al).

9.2.2 Motion-induced interruptions. The concept of motion-inducedinterruption (MII) was developed (Baitis et al) to quantify the effects oflocal, mainly lateral, motions which cause a person to lose balance orslip, and thus interrupt any task they may be performing. A frequencydomain technique, known as the Lateral Force Estimator (LFE), provides ameans for estimating the incidence of such interruptions and hence forsetting appropriate limiting values for task performance, or for evaluatingthe degree of degradation in performance when the levels of applied motionsexceed specified limits.

Extension of the technique is required to include non-lateral motioneffects, tasks involving major force requirements, eg manual reloading ofweapons and tasks performed by the seated operator. The current methodassumes a standing operator applying relatively small forces.

9.2.3 Motion-induced fatigue. Motion-induced fatigue, which should bedistinguished from the fatigue and malaise induced by motion sickness, isprimarily due to the need of having to continually compensate for wholebody displacement and in order to preserve suitable postures for task andother activities. In ships at sea, the primary contributory factor isconsidered to be the following motions experienced.

Although ISO 2631 describes a "fatigue-decreased proficiency boundary",this is not well-founded and the designer is advised to consult anappropriate source of expertise regarding the likely effects ofmotion-induced fatigue on the performance of any specific task.

9.3 Effects of motion and motion illness on task performance. Theestimation of the adverse effects of motions on task performance iscritically dependent on consideration of exposure duration. Motionsickness shows some recovery with increasing exposure duration, asdescribed, but fatigue, motion-induced interruptions and continuousvibration are likely all to have cumulatively adverse effects on well-beingand task performance. Their combined influences are likely to be at leastadditive.

The malaise resulting from motion illness can result in complete withdrawalfrom a task. Conversely, ‘some individuals’ task performance may beunaffected, even though they report quite severe symptoms of sickness. Theeffect of motion sickness itself can thus range from 0%, no change, to100%, complete degradation (Strong). These effects are at least partiallyindependent of type of task. Changes in performance of sensory tasks, egvision or hearing, motor tasks, eg tracking, writing or lifting and loadingactivities, or cognitive processing, eg memory or decision making, may becomparable where the primary influencing factor is disinterest due tomotion sickness malaise.

In contrast, the performance of short-term tasks with major motor (wholebody) movement requirements is likely to be adversely affected primarily by

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9.3 (Contd)

motion induced interruptions alone. Calculations indicate that acceptablelevels of MIIs of one per minute or below are equivalent to appliedaccelerations of approximately 0.11g (rms) or less. MIIs of five or moreper minute (0.16-0.17g) are considered extremely hazardous.

Longer-term tasks of whatever sort, eg helicopter maintenance on ships;sensor operation; repeated weapon loading activities, are likely to beaffected by a combination of MII and fatigue, together with motion sicknessif personnel are unadapted. No precise predictions are possible because ofthe complexity of the effects and the influence of individual task -specific parameters. In general, however, it is likely that tasks havingrestricted needs for taking in information and only a small motorcomponent, will be the ones least affected by motion.

9.4 Implications for vehicle, equipment and task design. For conventionalvehicle and platform designs, little scope may exist for dramaticimprovement by the elimination of provocative motion characteristics.Unconventional designs which substantially reduce motion at particularfrequencies will be of assistance, however, eg marked attenuation of majorfrequency peaks below 0.7 Hz will substantially ameliorate the incidence ofmotion sickness.

Stabilization of the whole platform, or isolation of specific workstationson stabilized or damped mountings may be of benefit. Bittner and Guignardsuggest this and other techniques to help reduce adverse motion influences.

Steps can be taken to locate critical workstations and tasks near to thecentre of gravity of the vehicle, to reduce the rotational movements aboutthe primary axes.

Head movements can be minimized by appropriate placement of visual tasksand displays (and associated controls) at each workplace, since this willreduce the severity of motion sickness symptoms. Head rests for seatedoperators may also be of benefit.

Operator workstations should be aligned with the principal axes of motionof the vehicle, ideally along the longitudinal (x) axis, thereby facingeither directly forward or to the rear.

Where possible, an external visual frame of reference should be availableto aid visual stabilization and to provide an external reference forpredicting repetitive motion changes. This may be possible using displaytechniques where a view of the outside world is not possible, eg theMalcolm horizon (Malcolm) or contact analog displays (Roscoe).

Where tasks require delicate movements, control techniques which showgreater resistance to motion should be chosen. McLeod and Griffin describealternative methods and their sensitivity to motion. Arm and wristsupports will be important to help ameliorate the effects of jolting andother sudden movements. Substitution of relatively gross physicalmovements, eg whole circuit board replacement, for fine manipulativeactions, eg circuit board touble-shooting in-situ, will be advantageous.

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9.4 (Contd)

For moving heavy loads in adverse motion conditions hand holds on fixedequipment and on the loads themselves will be of assistance. Where bothhands are required for this task, a body harness or support should beconsidered.

Where it is anticipated that adverse effects of motion are likely to remaindespite ameliorative measures, automation of the task should be considered.

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Section Six. Vibration and Shock

10 Vibration

10.1 Vibration is any sustained mechanical oscillatory disturbance,whereas shock or jolt is a transient mechanical disturbance. In thissection, consideration is given to the non–auditory effects ofenvironmental vibration and shock having frequency components within therange 0.06 to 1000 Hz.

Transportation devices, whether over land, on the sea or in the airinvariably expose the occupants to vibration which, depending upon theintensity and direction of the stimulus, the frequency spectra of thevibration and the duration of exposure can impair operational efficiency.Likewise, vibration transmitted to the occupants of buildings or off-shorefixed structures, either from machinery within the building or from thedynamic response of the structure to external forces (eg wind and/orwaves), can cause discomfort and degrade working efficiency. Disturbanceby mechanical shocks occurs during industrial activities, such as piledriving and blasting, as well as in military operations on detonation toexplosive charges. Gunfire from automatic weapons engenders a mechanicalstimulus that may be classified either as repeated shocks or as vibrationwith a high crest factor (ie ratio of peak acceleration to root mean squareacceleration).

Vibration and shocks may be transmitted to the body through, for example,the feet of a standing person, the buttocks, back and feet of a seatedperson or the hand(s) when using a vibratory tool such as a chain saw. Theadverse effect of a particular vibration environment is thus dependent notonly upon the physical characteristics of the vibration stimulus but alsoupon the dynamic characteristics of the interface between the individualand vibrating structure (eg compliance and damping of a seat cushion) andupon the posture, orientation and muscle tone of the subject. In theperformance of certain tasks it is the vibration of displays or handcontrols rather than of the operator that is of critical importance.

10.2 Effects of vibration and shocks

10.2.1 The principal effects of vibration and shocks on man can becategorized as:

(a) degradedexposure);

(b) impaired

(c) impaired

health and injury (which may be immediate or follow long-term

task performance;

comfort;

(d) motion sickness.

10.2.2 It must be recognized, however, that many variables influence humanresponse to vibration and shocks, these include:

(a) intrinsic factors:

(i) body size and build (age, sex, stature, etc);

21


10.2.2 (Contd)

(ii) body posture;

(iii) seating and restraint;

(iv) activities and nature of task performed;

(v) experience, expectation, arousal and motivation.

(b) extrinsic factors:

(i) physical characteristics of acceleration stimulus (magnitude,frequency spectrum, direction);

(ii) input location of stimulus;

(iii) duration of exposure;

(iv) other environmental factors (noise, heat, illumination etc).

Precise guidance on the effects of vibration and shock is thus rarelypossible, but the relevant British Standards (see annex A) provideinformation which should assist the designer in quantifying the mechanicalstimulus to the subject and the exposure dose, annexes to the Standardsgive broad guidance on the effect of a defined vibration or shock stimulusand provide sufficient information to guide the designer on how to minimizethe deleterious effects of vibration.

When using the data and "limits" presented in the annexes to the BritishStandards it is important to bear in mind the restrictions and constraintsplaced on their application. The "limits" are for guidance only. As notedabove, there are many factors which influence the effect of vibration andthese are frequently highly dependent upon the task being performed. Thusan analysis of the task must be made before any useful generalizations onthe influence of vibration and shock on task performance can be obtained.Information on the effect of vibration on some specific tasks is to befound in the scientific literature referenced in the annexes to the BritishStandards and by Griffin et al.

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Section Seven. Weightlessness

11 General

11.1 Stationary objects on the surface of the earth are subject to aconstant linear acceleration of 9.81 m/s2 or 1 g. This gravitationalacceleration may be nulled, such that the object experiences anacceleration close to 0 g:

(a) transitorily (< 1s) on being dropped, ie in free fall in theatmosphere;

(b) for periods of 10-40s during flight in a Keplerian (parabolic)trajectory in an aircraft;

(c) for prolonged periods during orbital (space) flight.

In a zero or more precisely a microgravity environment in which thelinear acceleration is typically less than objects becomeessentially weightless and there is no reactive force between the objectand the surface upon which it is placed. Likewise there is no friction tostabilize the position of the object on a surface unless an external force,with a component normal to the surface, is applied. An object, not incontact with a surface will maintain its position until acted on by aforce, whereupon it will be accelerated and, depending upon the mass of theobject and the magnitude and duration of the force applied, will achieve avelocity that will be maintained until acted upon by an opposing force todecelerate it and bring it to rest.

11.2 Human factors in weightlessness. Microgravity imposes certainconstraints on human activity and imposes special Human Engineeringrequirements, these may be summarized:

11.2.1 Spatial orientation. The absence of a gravity reference and henceno stimulation of the otolith organs of the vestibular apparatus,necessitates orientation within the vehicle being achieved solely by visualand tactile cues.

11.2.2 Task performance. Patterns of motor activity employed on earth forlocomotion, for the maintenance of posture and for the performance ofcertain movements, may no longer be appropriate in microgravity. Oninitial exposure to weightlessness difficulties may be experienced andworking efficiency decreased (typically by 30% during first day in orbit),but new patterns of sensory–motor co-ordination are acquired relativelyrapidly (2–7 days) and thereafter many tasks may be performed with anefficiency comparable to that achieved during ground-based training.Performance may also be degraded during the first few days inweightlessness because of motion sickness-like symptoms (space sickness)and discomfort due to venous congestion of the head and neck.

11.2.3 Controls and displays. Most human engineering criteria for thedesign of controls and displays for use in 1 g (as detailed in othersections of this Standard) are applicable for zero g use. Controls anddisplays should, however, be able to withstand crew-imposed loads, such asmay be imparted by a free-floating crew-member on moving himself or a heavymass from one position to another in the vehicle.

23


11.2.4 Restraint and temporary fixation. Provision has to be made for therestraint of crew members when performing tasks and for the tethering ortemporary fixation of tools and implements that are used. The forces thatcan be a development by voluntary muscular contraction in weightlessnessare similar to those achieved on earth (see section three), but thesemanipulative forces can be achieved only if structures and devices capableof withstanding the reactive forces are provided. Loss of muscle strength,particularly of extensors, may decrease with prolonged exposure toweightlessness, but this effect is largely prevented by appropriate dailyexercise in flight.

11.2.5 Habitability. Space vehicles present problems similar to those ofother environments in which humans have to live in an enclosed space withintegral life-support systems (eg submarines) and the same or even morestringent constraints and standards for the maintenance of the thermal andgaseous environment apply (see section two). In addition, specialfacilities have to be provided for essential activities, such as foodpreparation, ablution, urination, defaecation and sleeping.

11.2.6 Safety. The space vehicle and its payload present numerouspotential risk situations which directly or indirectly affect the safety ofthe crew or ground personnel. Safety standards are related to ten basichazard groups, namely:

(a) collision;

(b) contamination;

(c) corrosion;

(d) electrical shock;

(e) explosion;

(f) fire;

(g) injury and illness;

(h) radiation;

(i) temperature extremes;

(j) loss of re-entry capability.

Extensive safety guidelines have been prepared by both the NationalAeronautics and Space Administration (NASA) and the European Space Agency(ESA) to whom enquiry should be directed for current obligatoryrequirements and recommendations.

11.2.7 Physiological adaptation to weightlessness. Physiological changesoccur in a number of bodily systems during space-flight. Significantadaptive changes are detectable in:

(a) fluids and electrolytes;

(b) the Neurovestibular System;

24


11.2.7 (Contd)

(c) the Cardiovascular System;

(d) the Haemopoetic System;

(e) the Skeletal System;

(f) the Sensory-Motor System.

These processes are appropriate to the microgravity environment and, ingeneral, are not detrimental to efficient performance in flight. They are,however, disadvantageous on return to earth and normal gravity. After aspace-flight of several weeks’ duration the cardiovascular deconditioningand the alteration in sensory-motor control and postural activity can be asignificant impediment to operational efficiency until readaptation to thenormo gravic environment is achieved.

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Section Eight. Effects of Noise

12 General

12.1 Noise affects human health and performance in a number of ways.Apart from such environmental considerations as annoyance to the communityat large, which lie outside the scope of this Standard, the most importantand best researched effects are those on speech communication and onhearing acuity. The effect of noise in masking speech communication andother wanted sounds is considered in detail in part nine of this DefenceStandard.

12.1.1 The effect of noise on hearing is to produce a permanent andincurable loss of hearing acuity, typically greatest around 4 Hz, whichincreases with increasing noise exposure and which combines with lossesfrom ageing or other causes. The magnitude of the loss varies betweendifferent individuals, and in susceptible individuals can lead both tosocial disability and an inability to perform tasks (especially tasks of amilitary nature) requiring good hearing. Noise-induced hearing loss inService personnel can therefore lead to medical down-grading or, in extremecases, discharge. There is no completely "safe" noise exposure, and themaximum permitted exposure is therefore a compromise between the risk ofhearing loss and the technical difficulties in reducing noise exposure; ittherefore follows that noise exposure should always be reduced as far as isreasonably practicable.

12.1.2 Other effects of noise include:

12.1.2.1 Psychological effects on performance. The effects, most evidentat levels above 90 dB(A), depend very much on the nature of the task; ingeneral, performance on simple repetitive tasks is unlikely to be as badlyaffected as performance on more intellectually demanding tasks. The topichas been reviewed by Broadbent.

12.1.2.2 Effects on general physical health, other than on hearing. Thesehave proved very difficult to quantify (Burns 1979). However, it appearsthat limits set in respect of noise-induced hearing loss will also protectagainst other effects on health.

12.1.2.3 Sleep disturbance and general annoyance to off-watch personnel inliving spaces.

12.2 For hearing conservation purposes, continuous noise (from machinery,vehicles, aircraft etc) is measured either in terms of A-weighted soundlevel expressed in dB(A), or in terms of equivalent continuous sound level(8 hour), usually written as Leq (8 hour) and also expressed in dB(A).

The use of Leq is described in British Standard 5330 (BSI). It can beregarded as an average level referred to a nominal 9 hour period; seetable 1. Some equipment can make direct measurements of Leq.

The "A" in dB(A) refers to the A frequency weighting applied to themeasuring system; it is described, together with other requirements forsound level measurements, in British Standard 5969. The quantity L EP, dis similar to Leq, except that it takes no account of any hearingprotection which may be used.

26


12.3 The limit to noise exposure set by the Defence Standard is an 8 hourL e q at the ear of 85 dB(A); this Leq

shall not be exceeded during any24 hour period.

It is, however, strongly recommended that, as far as possible, the soundlevel at the ear should not exceed 85 dB(A). Exposure to noise must in anycase be reduced to the lowest level reasonably practicable.

The use of Leq is only possible where the exposure duration can be defined.Note that, where noise exposure results from use of more than one item ofequipment, both the level and the Leq should be derived from all noisesources, not from one item of equipment only.

Where noise exposure is of short duration, an Leq of 85 dB(A) implies soundlevels considerably above this value; this may cause a performancedecrement even where the effect on hearing is within the requirements ofthis Standard.

Levels below 85 dB(A) may be necessary where the ability to hear speech orother sounds is required; see part nine of this Defence Standard.

12.4 Measurement of impulse noise from weapons and other explosive sourcespresents special problems and equipment intended for measurement ofcontinuous noise is not suitable. Detailed guidelines for the measurementof impulse noise in Appendix 1 to the final report of NATO DRG Panel 8Research Study Group 6 (NATO). This Defence Standard, in common with CivilStandards, does not consider limits to personnel exposure from impulsenoise; however, limits are given in Defence Standard 00-27.

12.5 Use of hearing protection. In principle, the use of hearingprotection (ear plugs, ear muffs or noise-excluding helmets) can give avery substantial reduction in noise exposure, depending on both the natureof the protector and the frequency content of the noise. In practice, theuse of personal hearing protection gives rise to a number of problems (fora detailed discussion, see Alberti):

12.5.1 The protection, measured in practical usage, is generally less thanthat measured in ideal laboratory conditions specified in such standardmethods as British Standard 5108.

12.5.2 Protectors can be fragile and will deteriorate over prolonged use.Ear muffs in particular tend to clash with other headgear, such as safetyhelmets. Some protectors are very uncomfortable to wear. BritishStandard 6344, Part 1 specifies minimum requirements for ear muffs; anotherpart of this Standard is planned to consider ear plugs.

12.5.3 While persons of normal hearing are able to hear speech in noisysurroundings as well with protectors as without, persons with impairedhearing (noise-induced hearing loss, for instance) will have severedifficulty in hearing speech and other wanted sounds (including warning orcautionary signals) while using hearing protectors.

It is therefore necessary to reduce noise exposure by other means (such asreduction of noise at source, or location of personnel away from noisyareas) as far as is practicable; only if the noise exposure remainsexcessive should the use of hearing protection be considered. The

27


12.5.3 (Contd)

manufacturer shall advise the equipment procuring authority of anyrequirement for hearing protection.

12.6 Checklist

12.6.1 Has the noise exposure in areas likely to be occupied been measuredor estimated?

NOTE: Where equipment is to be installed in a workshop or other space,noise will depend on the acoustic characteristics of the space. In thiscase, prediction of the noise may be aided by measurements of sound powerfrom the equipment.

12.6.2 Will personnel exposed to the noise need to communicate by voice,or need to hear other auditory signals? If so, consult part nine of thisDefence Standard.

12.6.3 Will off-duty personnel be exposed to noise?

12.6.4 Will personnel exposed to noise have to perform complextasks?

12.6.5 Will personnel be exposed to noise from other sources?

mental

If so,combined exposure should be considered, not merely exposure from theequipment under consideration. Remember that speech and other noisetransmitted by communications systems adds to the total noise dose.

12.6.6 What steps have been taken to reduce noise from the equipment, orto remove personnel from noisy areas?

12.6.7 Is the noise impulsive, or does it contain impulsive components(eg from gunfire or explosions)?

12.6.8 If, after all practicable means of noise reduction have beenemployed, unprotected noise exposure approaches or exceeds an Leq (or, ifduration is undefined, a level) of 85 dB(A):

(a) Has the procuring authority been informed of the need for personnelhearing protection?

(b) Have the practical problems associated with the use of hearingprotection been considered? What solutions are offered?

(c) Can the noise reaching the ear be reduced to 85 dB(A) by use ofprotection?

(d) Are the communication problems likely to be encountered by some usersacceptable?

(e) If special forms of protector, eg incorporating communicationfacilities, are required, has procurement action been initiated?

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Table 1

Relation Between Sound Level and Durationfor an L of 85

eqdB(A)

SOUND LEVEL DURATION

80 dB(A) 24 hours82 dB(A) 16 hours85 dB(A) 8 hours86 dB(A) 6 hours88 dB(A) 4 hours91 dB(A) 2 hours94 dB(A) 1 hour97 dB(A) 30 minutes100 dB(A) 15 minutes

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Section Nine. Darkness and Dazzle

13 General

13.1 The human eye is an extremely versatile sensor. Most people possessthe ability to perceive a broad range of colours and have a high degree ofacuity (see section six, Vision and Lighting, clauses 6 and 7).

13.2 In addition the human eye can function very effectively over aconsiderable range of ambient illumination, from bright sunlight (10

7 lUX)down to starlit night and lower (approx l0-5 lux). At the extremes of thisscale the brightest tolerable light is 1012

times that of the lowestbrightness necessary to produce the sensation of light. There are twoconsequences of this range which are of particular significance in militaryoperations. One is that at night the colour system of the eye does notoperate and secondly a period of adaptation is required for efficientvisual functioning in the dark after leaving a lighter zone. The period ofadaptation required in the light, after leaving a relatively dark area, isconsiderably less.

The implications of this are readily obvious if naked eye surveillance mustbe undertaken at night after leaving a brightly-lit room, or if viewingthrough an image intensifier is succeeded by naked-eye viewing.

13.3 For a detailed exposition of this topic, and practicable solutions,the reader is directed to Part six of this Defence Standard, clause 5(Light Sensitivity) and clause 30 (Illuminance Requirements for ParticularMilitary Circumstances).

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Section Ten. Effects of Radiation


14 Ionizing Radiation

14.1 Radiations that cause ionization, either directly or indirectly,include the electromagnetic X and gamma rays, alpha and beta particles,protons, neutrons and certain other particles are of no practicalsignificance. There is a natural background of ionizing radiationoriginating from cosmic radiation, the natural radioactivity of the earthand from radioactive substances naturally present in our bodies. Alpha andbeta particles have a short range, particularly in tissue and are emittedprincipally from radioactive isotopes. The greatest hazard in this case isfrom taking the isotope into the body by inhalation, ingestion or thecontamination of wounds. Neutrons generally originate from nuclearreactions, particularly fission. They have a long range in air andpenetrate tissue fairly well where they indirectly cause ionization andthus damage cells. They are particularly potent in causing certain longterm damage such as inducing cancer or cataracts of the lens of the eye.For example, they are considered to be at least 10 times more able toinduce cancer, absorbed dose for absorbed dose, than X or gamma rays.Gamma rays originate from the nuclei of radioactive isotopes. They have along range and penetrate tissues with increasing ease with increasingenergies (measured in thousands or millions of electron volts, KeV or MeV)where they cause damaging ionizations of molecules. X-rays are virtuallyidentical to gamma rays although often of a lower energy, their source isthe only difference as they do not arise in the nucleus of an atom but fromthe electrons orbiting the nucleus. The unit of absorbed dose is the GrayGy) which equals 100 of the old rad units, for biological effects theabsorbed dose equivalent is used for which the unit is the Sievert (Sv)which equals 100 of the old rem units.

14.2 Biological effects of ionizing radiations. The ionization of humantissue will be damaging to some degree depending on the amount (ie absorbeddose), its type (ie absorbed dose equivalent when absorbed dose ismultiplied by a quality factor, eg 10 for neutrons) and the dose rate. Thelonger the period of time over which a fixed dose is received the less willbe its effect. The volume of the body irradiated is also important. Ifonly part of the body is irradiated the effect is less.

The effects of ionizing radiation are divided into two. Some occur atrandom, eg induction of cancer or genetic defects, where increasing dosesincrease the chance of developing an effect. These include theparticularly radiosensitive bone marrow whereabout 5 Sv (acute dose) wouldcause such depression of blood cells that about 50% of those exposed woulddie within 2 months. Other effects include skin damage similar to burningparticularly from beta emitting isotopes on the skin and damage to thelining cells of the gastro-intestinal tract causing gastro-intestinalsymptoms.

After an acute whole body dose of penetrating ionizing radiation in the3 to 5 Sv range there will be a period of between 0.5 and 3 hours withoutany symptoms. This will be followed by a period of 12 to 48 hours ofnausea, some vomiting, possibly some diarrhoea. This will pass and thepatient will seem quite well but blood tests will reveal a falling whitecell count. After 2 to 3vomiting, diarrhoea, with

weeks there will be a recurrence of nausea,loss of hair, bruising and a risk of death from

31


14.2 (Contd)

infections or possibly bleeding. Higher doses shorten this timescale untilafter some 10’s of Sieverts, brain effects (coma etc) cause a death withinhours or at the most a few days.

It is believed that any dose of radiation, however small if given tosufficient numbers can cause cancer or leukaemia. The best estimateavailable at present is that 10,000 person Sieverts (eg 0.1 Sv to each of100,000 persons or 0.01 Sv to each of a million persons) will cause aboutan additional 125 cancers in the period of between 10 and 40 years afterthe exposure. A further 40 cases of hereditary ill health will also beproduced in the first 2 generations. Because of a lack of any evidence fora threshold below which no long term random risks arise, a basic tenet ofradiological protection is that all doses shall be kept "As Low AsReasonably Achievable" (ALARA).

— — -- -

14.3 Protection against ionizing radiation. The three basic principles ofprotection are time, distance and shielding. The shorter the time exposedto a certain dose rate the less the dose will be. The further away from asource of radiation, the lower will be the dose rate due to the inversesquare law and absorption of the radiation in air or other materials.Shielding requirements depend on the type of radiation:

(a) Alpha. A piece of paper will stop alpha particles, as will intacthuman skin. Prevention of intake into the body is the prime concern.

(b) Beta. Perspex, glass, aluminium etc will completely absorb betaradiations if about 10 mm thick. The thickness required depends on theenergy of the beta particles.

(c) X and Gamma Rays. Dense material such as lead will reduce theintensity of these radiations but may need to be very thick to reduce themto acceptable levels.

(d) Neutrons. Materials containing a high proportion of hydrogen atomsare best at slowing down neutrons. Water, polythene and concrete areexamples but these may need to be several metres thick. Once slowed,substances such as boron can be used to absorb these slow neutrons butinteractions with other substances can produce high energy gamma rays whichwill require lead or similar shielding.

Personnel dosemeters (thermoluminescent materials have largely replaced thefilm badge) are used to measure the dose of radiation received byindividuals. But if there is a significant dose rate or radioactivecontamination hazard, appropriate instrument measurements are necessarybefore personnel are permitted to work in the area.

14.4 Radiofrequency and other non-ionizing electromagnetic radiations.There is a wide spectrum of electromagnetic radiations, unable to causeionization, ranging in frequency from ultra-violet light (3 x 1016

Hz infrequency, 10-8 metres in wavelength) down to power frequencies (50 or60 Hz). The amount of absorption and depth of absorption of this energydepends on frequency/wavelength. In all cases the hazard is due to heatingof tissues, varying from sunburn of the skin from ultra-violet to wholebody heating in the 30–300 M Hz region. The lens of the eye and the testes

32


14.4 (Contd)

are particularly sensitive to heating hazards. Above a specific absorptionrate of 4 WKg-1

there is clear evidence of harmful effects and thus limitsare based on a fraction of this, in the case of the USA, one tenth(0.4 WKg-1). UK limits will be the subject of an EEC directive in duecourse. Lasers can also produce similar harmful heating effectsparticularly affecting the eye. Lasers are classed from a hazard freeclass I to the most hazardous class IV.

33


Section Eleven. Chemical and Biological Contaminants

15 General

15.1 Two aspects of chemical and biological contaminants should beconsidered: (a) equipment, and (b) the human operator.

15.2 Equipment. Equipment used in the field is likely to becomecontaminated by a variety of agents and will require decontamination.Particular attention should be paid to case design and the construction ofswitches, knobs, displays etc. Comprehensive design information is givenin "A Guide to the Chemical Hardening of Equipment", Chemical DefenceEstablishment Technical Memo 79, 1986.

15.3 Human Operators. The presence or threat of chemical and biologicalcontaminants require the human operator to use defensive measures which canimpair his efficiency and hence performance. The measures are (a) physicaland (b) pharmacological and the impairments may be physical, physiologicaland psychological, or all three.

15.3.1 Physical defence is provided by Individual Protective Equipment(IPE) comprising a smock with hood, trousers, plastic overboots, innercotton and outer synthetic rubber gloves and a respirator (currently S6 orS10).

15.3.1.1 Physically, IPE is bulky; it restricts movement and increases theeffective size of the body, hands, feet and head by as much as 50%. Also,the respirator restricts peripheral vision and the wearer needs to turn hishead more than normal. Equipment should allow adequate access room forhands, fingers and feet and extra room for the head to allow for bothaccess and movement.

15.3.1.2 Physiologically, IPE reduces the capacity for sustained physicalexercise progressively with time as the ambient temperature and humidityincrease. Equipment should involve the minimum of heavy and/or sustainedphysical effort, particularly if intended for use in hot, humid climates.

15.3.1.3 Psychologically, IPE attenuates and distorts perception and thusaffects the ways in which information should be conveyed to the operator.Hearing is attenuated and distorted by the hood and auditory information,particularly that in the speech frequency range, may require amplificationor filtering. Peripheral vision is distorted and the visual field isnarrowed by the respirator eyepieces (foveal vision may be distortedslightly depending on direction of gaze). Visual information should bedesigned for foveal vision in the photopic range and symbols should subtenda minimum visual angle of 20 minutes of arc. Peripheral vision should notbe used except to direct attention. Visual displays should also makeallowance for the respirator bulk and eyepiece design. Touch, and therebyfinger dexterity, are severely impaired by the glove assembly; switches andother controls should be large and widely spaced (see above under physicalimpairments) with a positive amount and resistance of mechanical movement.

Research into the physiological and psychological effects of wearing IPE isstill in progress. Details may be obtained from the Chemical DefenceEstablishment and the Army Personnel Research Establishment.

These effects of IPE may well interact with other environmental factorssuch as visual and auditory noise.

34


15.3.2 Pharmacological defence is provided by pretreatment and therapeuticdrugs. It is impossible to give specific guidelines regarding these sincethe effects vary with a multitude of factors and research and developmentis still in progress. However, some general points can be made.

15.3.2.1 There is no evidence that the current pretreatment for nerveagent poisoning (NAPS) produces any significant behavioural impairment atthe dose available and NAPS may be ignored for the purposes of equipmentdesign.

15.3.2.2 The current therapy for nerve agent poisoning comprises a mixtureof drugs which, together or separately, will impair performance in wayswhich could be significant for equipment designers. The drugs are combinedin a self-injection device and up to three doses may be administered. Theeffects are generally mild following one injection and increase in severitywith further injections. They include impairment of visual perception,decision-making processes, memory and response co-ordination. Equipmentdesigners should allow for the effects of up to two injections. Generally,this means that normal ergonomic guidelines should be followed with extraallowance for imperfect performance. Visual displays, markings,instruction etc should be large and clear to allow for blurred vision. Therelationships between displays and controls should be simple andunambiguous to allow for slowed decision processes. Sequences forinstructions and operations should be clear and short to allow for impairedmemory. Controlsimpaired responseand psychologicalobtained from the

should be large and widely separated to allow for co-ordination (see above). Research into the clinicaleffects of drugs is still in progress. Details may beChemical Defence Establishment.

35

NT DEF STAN 00-25 (PART 5)/1

Section Twelve. Safety Standards

16 Guidelines

16.1 Guidelines on safety of equipment for use by the Services may readacross from the civilian situation. The Health and Safety at Work etcAct 1974 applies to all employees including those in control of members ofthe armed forces, designers, manufacturers, importers and suppliers ofarticles and substances for use at work by employees and to persons incontrol of premises, including vehicles and tents, occupied by employees atwork. Members of the armed forces are not exempt, although in practice theHealth and Safety Executive only inspects premises and activities which arenot classified as “operational”. It must be remembered that equipmentdesigned for use under operational conditions will also need to be used ina training, non-operational situation.

16.2 The general standard of safety of equipment premises and systems ofwork for use by the armed forces is thus at least the same as for any otheremployee. Due regard must also be paid to the expected conditions of work,which could be harsher than in civilian life and to the tacticalconsequences of a failure of either the equipment, the method of work orthe operator. These considerations will lead to a decision on the standardof safety to be aimed for by the designer and others.

16.3 There is a wide amount of literature on hazards at work, andStandards are specified for many situations. Details are contained instatutes (Acts, Regulations and Orders), Codes of Practice and GuidanceNotes issued by the Health and Safety Commission and Executive and inStandards and other documents issued by national Standards houses, tradeand professional associations and other civilian and military authorities.

16.4 The general procedure will be that the authority responsible forspecifying a defence equipment requirement will, in consultation with usersand planners if necessary, define the proposed conditions of use.Designers and suppliers will be responsible for providing information aboutthe safety of equipment under these conditions and under other foreseeableconditions including partial equipment failure and misuse by operators.They will be responsible for obtaining research data if this information isnot already available. It is probable that a dialogue between designers,suppliers etc on the one hand and the procurement authority, together withtheir operational and human factors advisers, on the other hand will beestablished during the design and development of more complex items ofequipment. This procedure could include an analysis of possible hazardsleading to refinement of the design and to recommendations for a system ofwork and training methods.

36


Section Thirteen. Thermal Environments

17 General

17.1 A number of national and international standards are relevant sourcematerials for designers who seek advice and guidance concerning thermalenvironments. Further details are given under the headings below.

17.2 Units and Measurements. ISO 7726 contains internationally agreeddefinitions and methods of measurement of heat and cold. This Standardshould be consulted for guidance on these matters. Ambient temperaturesare correctly specified in degrees Centigrade (Celsius), and although airtemperature may be measured with a conventional thermometer this is not asufficient description of the thermal environment. Details are provided inISO 7726. One generic way to describe the thermal environment is by meansof Effective Temperature. It is important to note that there are severalEffective Temperature scales, the most recent being designated ET. Thisscale of subjective temperatures has superseded all others (see NOTE).

NOTE: Effective Temperature is equal to air temperature when the RelativeHumidity is 50%, the air movement is 0.1 metres per second and when thewalls of the room are at the same temperature as the air.

17.3 Table 2 below gives typical human responses to a range of effectivetemperatures.

Table 2

Typical Human Responses to Effective Temperature

°F °C RESPONSES

110 43 Just tolerable for brief periods.

90 32 Upper limit of reasonable tolerance.

80 26 Extremely fatiguing to work in. Performancedeteriorates badly and people complain a lot.

78 25 Optimal for bathing, showering. Sleep is disturbed.

75 24 People feel warm, lethargic and sleepy. Optimal forunclothed people.

37


Table 2 - Continued

°F °C RESPONSES

72 22 Most comfortable year-round indoor temperature forsedentary people.

70 21 Optimum for performance of mental work.

64 18 Physically inactive people begin to shiver. Activepeople are comfortable.

60 16 Manual dexterity impaired (stiffness and numbness offingers).

50 10 Lower limit of reasonable tolerance.

32 0 Risk of frost-bite to exposed flesh.

17.4 Heat stress. Heat stress may be defined as the loading whichcircumstances impose upon the thermoregulatory mechanisms of the human body(Pheasant 1987). The degree of heat stress is a function of a number offactors; physical workload, thermal insulation of clothing, airtemperature, thermal radiation from nearby surfaces, air humidity, and airspeed. the currently favoured index is the Wet Bulb Globe Temperature(WBGT) index as defined in ISO 7243. An alternative, more sophisticated,method of calculating heat stress, based upon predicted sweat rate, isgiven in ISO 7933.

17.5 Thermal comfort. Thermal comfort is defined in ISO 7730 as "thatcondition of mind which expresses satisfaction with the thermalenvironment". ISO 7730 is based upon the work of Fanger in the USA andcontains detailed equations which relate metabolic rate, clothing and anumber of environmental factors to the subjective feelings of comfort of atypical group of people.

ISO 7730 specifies two indices; Predicted Mean Vote (PMV) on a particularcomfort rating scale, and the Predicted Percentage, of people, who would beDissatisfied (PPD).

38


17.5 (Contd)

ISO 8996 gives guidance on metabolic rate determination, whilst ISO 9886and ISO 9920 give information concerning thermal strain, and estimation ofthermal characteristics of clothing ensembles. At the time of writing(1991) each of these latter two Standards is a Draft for Discussion.

17.6 Cold Stress. The most serious risks associated with cold stress arefrost-bite and hypothermia.

Frost-bite occurs when flesh is exposed to sub-zero temperature.Hypothermia is a fall in body temperature. Suitable clothing, andappropriate space heating, should be capable of preventing either of theseconditions. The cooling power of an environment is commonly expressed inthe Windchill Scale.

KO is windchill factor

V is air speed in metres per second

Ta is air temperature (°C)

The table below gives a rough guide to the interpretation

Table 3

Interpretation of Windchill Index (KO)

of windchill.

KO

< 9090 to 150150 to 300300 to 500500 to 700700 to 900900 to 11001100 to 1300> 1300> 1650> 2150

17.7 Hot Surfaces. Livingtemperature reaches 43°C.

Interpretation

HotWarmPleasantCoolVery coolColdVery coldBitterly coldExposed fleshExposed fleshExposed flesh

freezesfreezes in one minutefreezes in 30 seconds

human tissue will be burned when its

The rate at which burning is initiated, and progresses, is dependent uponfactors such as object temperature, composition etc. A BSI publisheddocument, PD 6504, should be consulted for further information.

39


17.7 (Contd)

At present, there is only one British Standard which deals with maximumtemperatures for non-working surfaces. This is BS 4086, which relates todomestic cookers. An ISO Standard dealing with surface temperatures oftouchable parts is currently under discussion. A draft European Standardcovering hot surfaces is expected to be published in 1992.

40


Section Fourteen. Combined Environmental Stressors

18 Definition of Terms

18.1 Stress is a term used to refer to a situation or environment in whicha person is overtaxed in some way. Strain is the negative or pathologicaloutcome of stress.

Stressors - the environmental factors which produce a stress response in anindividual.

18.2 Introduction and definitions of interactive effects. Previoussections of this Part of the Defence Standard have examined the effects ofsingle environmental stressors or hazards. In a working situation,however, it is usual to find two or more of these stressors actingsimultaneously. This section refers to the overall effect of suchcombinations on an operator within a system. These stressors will interactin different ways to produce one of three types of outcome. Theinteractions are defined according to Murray and McCally and are describedbelow:

18.2.1 Additive effect. The combination produces a total effect which isequal to the linear sum of the single stressors.

18.2.2 Synergistic effect. The combination produces a total effect whichis greater than the linear sum of the single stressors.

18.2.3 Antagonistic effect. The combination produces a total effect whichis less than the single stressor or linear sum of the single stressors.

18.3 Factors affecting resultant stress. When assessing the effects ofexposure to combined stressors the following must be considered.

18.3.1 The severity of the stressors. The intensity of two or moreindividual stressors and their combined effects should be considered. Itis suggested that the resultant stress will depend on a person’s perceptionof which stressor is the most uncomfortable or has the over-riding effect.At certain levels stressors may also be stimulating and arousing, resultingin better performance. The precise levels will vary according to theindividual (see 18.3.2), complexity and duration of the task and type ofstressors present.

18.3.2 Individual differences. The levels of stress produced and thesusceptibility of the operator can determine the overall effect of thestressors. The effect on the individual will depend upon:

(a) previous experience;

(b) expectation;

(c) control over the stressors;

(d) type and complexity of task;

(e) experience at performing the task under stressors;

(f) motivation to succeed.

41


18.4 Stages in processing affected by stressors. The stressors areconsidered to act on the operator at the following points.

18.4.1 Input of information. The gathering of relevant information viavarious human senses can be inhibited by stressors. The effects areusually physical such as vibration affecting vision, or noise inhibitingreception of a signal.

18.4.2 Processing of information. Narrowing of attention and a reducedcapacity for internal rehearsal that may arise from exposure to stressorsare examples of information processing effects.

18.4.3 Response output. In most situations the operator has to respondand this, like input, may be affected by stressors. For example, vibrationmakes manual control tasks difficult.

18.4.4 The effects of stress on input and output are often immediate, butchanges in information processing may not be seen at once. To prevent adecrement in task performance an operator will often alter his strategy.This may mean a higher workload as more attention or central processing isemployed. Although performance of the immediate task is maintained, themore peripheral components of the task might suffer. Adding a second taskunder conditions of increased workload might also lead to a severeperformance decrement, or collapse of both.

18.5 Duration of exposure. As the effects of stressors on informationprocessing are usually time-dependent (see 18.4.4) they may not be apparentduring short periods of exposure. However, fatigue may arise from longperiods of exposure. This fatigue can be physiological and/orpsychological, affecting either the physical processes or centralprocessing.

18.6 Guide to outcome of exposure to combined stressors. The manydifferent interactions and effects listed in table 4 illustrate thedifficulty in predicting the outcome of any combination of stressors.However, the following points may be used as a guide.

18.6.1 The outcome of stressor combinations may possibly be predicted byconsidering the inverted U–arousal model as discussed in Hockey andHamilton (1983). This suggests that if the task is complex and/or workloadhigh the operator will be more aroused than if the task is simple and/orworkload low. In the former instance where arousal is already high, hewill be more susceptible to the effects of environmental stressors whichmay induce over-arousal. Although the operator may maintain performanceunder one stressor, the combination of more may well lead to degradation.Increasing one or more of the stressors in a combination will notnecessarily lead to a linear increment/decrement in performance.

18.6.2 The sensory inputs to the operator will not only relate to the taskin hand but will also come from the environment, eg noise, acceleration,vibration. Since he cannot attend to all these inputs the effect of thestressors may cause 'selective attention'. This may mean that importantinformation inputs are excluded. The greater the input load, the greaterthe degradation.

42


18.7 Interactive effects and guide to table 4. Table 4 shows theinteractive effects found between combined stressors. The interactionsstated make use of the definitions given in 18.2. The original papers havebeen examined and only the interactions which are clear and unambiguoushave been quoted.

Interactions shown in brackets are those descriptions used in the originalpapers if they vary from that found during verification. Lack ofuniformity in defining the interaction terms probably caused thisdiscrepancy in most cases. In others, insufficient information on singlestressor or control conditions meant that the interaction stated in thepaper could not be verified for this Standard. In this instance 'notverified' has been placed in the 'interaction' column.

Table 4

Stressor Interactions

STRESSORS OUTCOME OF DETAILS OF INTERACTION REFERENCEINTERACTION

Vibration Vertical vibration (2.6-16 Hz Antagonistic Harris andNoise 3.5 m/s2) and noise (100 dBA) produce effect Shoenberger

less of a decrement than the singlestressors in a complex counting task.

Tic effect Noise (100 dB) and vertical vibration Antagonistic Sommer andVibration (6 Hz 1.0 m/s2) give less of a effect HarrisNoise decrement in a tracking task

(horizontal and vertical error) thanvibration alone.

Vibration Noise (110 dB) increases the Antagonistic Harris andNoise decrement caused by vertical effect Shoenberger

vibration (5 Hz 2.5 m/s²) in a (Additive)tracking task but this is not equalto the sums of the single stressors.

Vibration Noise levels of 110 dB and vertical Additive Harris andNoise vibration (6 Hz 1.0 m/s2) produce an Antagonistic Sommer

additive effect in the vertical effectcomponent of a tracking task and an (Additive)antagonistic effect on the horizontalcomponent.

43


Table 4 - Continued


Vibration Vertical vibration (0.6-1.2 m/s2 rms) Antagonistic Sandover andNoise with noise of equal perceived effect Champion

intensity (78-85 dBA) produces aneffect on mental arithmetic scoreswhich is less than that of the singlestressors.

Vibration Semi-random vibration (1.6-4.0 m/s2 Not verified Dean et alNoise rms) and noise (112 dB) produce no

significant performance orphysiological effects in simulatedhelicopter flight.

Vibration Vertical vibration (2.5 Hz 2.3 m/s2) Not verified Ashley andNoise and noise (78 dBA) produce no Rao

vigilance task effects.

Vibration The only significant effect produced Not verified LoebNoise by two levels of noise and vibration

(6.5 m/s2 + 94 dB, 13 m/s2 + 102 dB)was on visual acuity.

Vibration Vertical random and horizontal Synergism RylandsNoise vibration (1.54 m/s2 1.08 m/s2) and

noise 94 dBA leq 5h produces asynergistic decrement in targetdetection and decoding times.

Vibration Combined heat (49 deg C), vertical (Antagonistic Grether etNoise vibration (5 Hz 2.9 m/s2) and noise effect) alHeat (105 dB) produce less of an effect

on tracking and RT tests than thesingle stressors or vibration andheat combined.

Noise Noise (90 dB) and heat (31 deg C Not verified Viteles andHeat Effective Temperature) produce no Smith

significant performance loss, eithersingly or combined.

44


Table 4 - Continued


Noise Noise (110 dB) and temperatures up Not verified Dean et alHeat to 43 deg C produce no significant

degradation in performance orphysiological thermal equilibrium.

Vibration Acceleration of 3.85G and vibration Not verified Clarke et alAcceler- at 11 Hz improves the visualation decrement associated with the same

vibration and acceleration of lG.

Vibration Tolerance to resonating frequencies Synergism VykukalLinear between 2.5 and 20 Hz is reduced by effectAcceler– high linear acceleration. Higheration mechanical impedance, greater

transmission of energy to internalorgans and pain were reported.

Positive Prior heat stress with minimal Not verified Taliaferro,Acceler- dehydration (l-3% body wt) lowers Wempen andation tolerance to acceleration (G value) WhiteHeat by 15-18%. Peripheral light loss

and poor co-ordination preventedlight detection.

Acceler- Heat (skin temp 37 deg C) reduces Not verified Martin andation tolerance to acceleration by lowering HenryHeat G value for peripheral light loss.

Upwards Prior heat stress with dehydration Not verified GreenleafAcceler- (4.3% body wt) lowers tolerance to et alation acceleration by decreasing the time

Dehydrat- to greyout.ion

Upward An environmental temperature rise Not verified BurgessAcceler- from 24 to 71 deg C reducesation tolerance to acceleration by 1G.

Heat Peripheral light loss and poorco-ordination prevented responseto target lights.

45


Table 4 - Concluded


Acceler- Cold (skin temp 25 deg C) increases Antagonistic Martin andation tolerance to acceleration over effect Henry

Cold 15 seconds by raising the G valuefor peripheral light loss.

Positive Hypoxia (9.5% inspired 02) reduces (Additive) BurgessAcceler- tolerance to acceleration by 18%ation lowers the G value for peripheral

Hypoxia light loss.

Hypoxia Hypoxia (23000 ft equiv) lowers the Not verified GauerUpward G value tolerated during accelerationAcceler- by 25%.ation

Hypoxia Hypoxia (18000 ft equiv) during cold Not verified BrownCold exposure, raises heart rate but the

effect was felt to be no more seriousthan exposure to each stressorsingly.

Hypoxia Hypoxia (10% inspired 02) and cold Not verified BullardCold (5 deg C) produces an apparent

synergistic increase in heart rateand ventilation rate. Shiveringincreased greatly during the first15 minutes of exposure.

Hypoxia Heat (49 deg C) and hypoxia (equiv Antagonistic HaleHeat 14000 ft) increases the cardio- effect

acceleration produced by the single (Synergisticstressors but does not exceed their effect)linear sum.

Hypoxia Heat (41 deg C), white noise Not verified Dean,Heat Noise (110 dB) and hypoxia (12000 ft equiv) McGlothlen

studied in pairs or all combined, and Monroeshow additive interactions.

Hypoxia Small amounts of CO reduce tolerance Not verified ArmstrongCarbon to hypoxia. Helps to promoteMonoxide unconsciousness.

46


Section Fifteen. Effects of Sleep Loss

19 Introduction

The purpose of this Section is to summarize the effects of sleep lossrelevant to designers; it is therefore not a fully comprehensive statementon the subject. Performance is impaired in many ways, with inability toconcentrate being central amongst them. This effect, together with periodsof difficulty in comprehension, misinterpretation, and feelings ofdisorientation, often appears after one night of total sleep loss, and ispresent in most individuals after 2 nights without sleep.

20 Lapses of attention

Inability to concentrate, or lapses of attention, are due to 'microsleeps'which last a few seconds; these short periods, when signals are missed,increase in frequency and duration with increasing sleep loss. Theselapses are responsible for much of the performance impairment which isfound following sleep-deprivation, especially in tasks that requirecontinuous attention.

21 Vigilance

Because of the occurrence of these lapses, it follows that vigilance isimpaired. Situations with little sensory stimulation increase sleep-losseffects; performance can be improved by the interjection of extra signalsand, for example, by using 2 sensory modalities together (vision andhearing) for the detection of targets when surveillance equipment is used.

22 Memory

Also impaired is short-term memory, and so aide-memoires are important.Because of deterioration in memory, tasks requiring long sequences ofactions need to have inbuilt devices which preclude order-of-events errors.Complex decision-making is also likely to be impaired if there is a longsequence of clauses to be remembered.

23 Long, uniteresting and monotonous tasks

Tasks that are long, uninteresting or monotonous are adversely affected byloss of sleep. Any variety, or change of stimulation, that can beintroduced into the situation will help to reduce the impairment.

24 Work-paced tasks

Tasks that are work-paced, as opposed to self–paced,by sleep deprivation; this is because an attentionalwith the need for a response.

25 High workloads

are adversely affectedlapse may coincide

Following sleep deprivation, performance during periods of high workload ismore impaired than during periods of low workload. This is because whenworkload is high there are few or no interludes, and so attentional lapseswill almost certainly coincide with a work requirement. Even a short breakin activity is very beneficial.

47


26 Tasks without feedback

Performance on tasks where there is little feedback will be adverselyaffected following loss of sleep, knowledge of results adds incentive.

27 Routine tasks

Routine but critical subsidiary tasks tend to be skipped; this is part of ageneral unwillingness to respond following loss of sleep. Addedinterest/incentive will assist personnel to carry out subsidiary tasks.

28 Speed of response

All tasks are likely to take longer following sleep deprivation, andreaction time to a stimulus is increased.

29 Erratic performance

Performance becomes more erratic, and there is increased variability inproficiency following loss of sleep.

30 Time of day

Performance is at its lowest ebb between 0200 and 0600with the low point in circadian rhythms. This drop inexacerbated by sleep loss.

31 Eyestrain

hours, coincidingperformance is

Under conditions of prolonged sleep deprivation there are likely to bereports of feelings of eye strain, headache, blurred vision and doublevision; these symptoms are particularly likely to occur during anyprolonged close work, especially under conditions of poor lighting (seePart 6, Vision and Lighting). Performance can be improvedof clear, well-lit displays (see Part 7, Visual Displays).

32 Physical tasks

The performance of physical tasks will only be affected insevere physical fatigue.

SUMMARY

33 Tasks most affected by sleep loss

by the-provision

the presence of

Complex, uninteresting, lengthy, requiring sustained attention, subsidiary,work-paced, entailing a long memory chain, demanding protracted viewingperiods at short range.

34 Tasks least affected by sleep loss

Short, simple, interesting, self-paced, physical.

48


35 Main effects of sleep loss on mental processes

Lack of concentrationLapses of attentionReduced vigilanceSlowing of actionImpaired short-term memoryDifficulty in comprehensionMisinterpretationDisorientation

49

Blank Page

INT DEF STAN 00-25 (PART 5)/1ANNEX A

Related Documents

The documents and Duplications referred to in this Part of the Standard areas follows:

IS0 2041ISO 2631

ISO 6897

ISO 7243:

ISO 7726:

ISO 7730:

ISO 7933:

ISO 8996:ISO 9886:

ISO 9920

BS AU183BS 1397

BS 3254BS 4086:

BS 6472

BS PD6504:

BS 6841

BS 6842

Defence Standard 00-25Defence Standard 00-27

Defence Standard 05-74

BR 1326BR 1326AJSP 390JSP 392

Vibration and shock - vocabularyGuide to the evaluation of human exposure towhole-body vibration.Guide to the evaluation of the response ofoccupants of fixed structures especially buildingsand off-shore structures to low-frequencyhorizontal motion (0.063-1Hz).Hot environments; estimation of the heat stress onworking man, based on the WBGT-index.Thermal environments; instruments and methods formeasuring physical quantities.Moderate thermal environments; determination of thePMV and PPD indices and specification of theconditions for thermal comfort.Hot environments; analytical determination andinterpretation of thermal stress using calculationof required sweat rate.Determination of Metabolic Heat Production.Evaluation of thermal strain by physiologicalmeasurements.Estimation of thermal characteristics of a clothingensemble.Passive seat belt systems.Industrial safety belts, harness and safetylanyards.Seat belt assemblies for motor vehicles.Recommendations for maximum surface temperature ofheated domestic equipment.Guide to Evaluation of human exposure to vibrationin buildings (1Hz-80Hz).Medical information on human reaction to skincontact with hot surfaces.Measurement and evaluation of human exposure towhole body mechanical vibration and repeated shock.Guide to measurement and evaluation of humanexposure to vibration transmitted to the hand.Human Factors for Designers of Equipment.Acceptable limits for exposure to impulse noisefrom military weapons, explosive and pyrotechnics.Guide to the practical safety aspects of the use ofradio frequency energy.Air Purification in submarines.Materials toxicity guide.Military laser safety.Instructions for radiological protection(section 12).

A-1

INT DEF STAN 00-25 (PART 5)/1ANNEX A (Continued)

Other Publications

Alberti P W (ed) Personal Hearing Protection in Industry RavensPress New York. American Conference ofGovernmental Industrial Hygienists (ACG1H)Armstrong H G Principles and Practices of Aviationmedicine (3rd ed) Baltimore: Williams and WilkinsCompany.

Ashley C and Effects of whole body low frequency random verticalRao B K N, vibration on a vigilance task. Paper presented to

Human Response to Vibration Conference, Sheffield.

Aviation Medicine - 2nd edition 1988 ed J Ernsting,P F King ButterworthLondonChapter 10: The effects of long duration

acceleration.Chapter 11: Protection against long duration

acceleration.Chapter 12: Crash dynamics and restraint systems.Chapter 13: Head injury and protection.Chapter 16: Escape from aircraft.

Baitis A E Applebee T R Human Factors considerations applied to operationsand McNamara T M of the FFG-8 and LAMPS mk III Naval Engineering

Journal 96(4) pp 191-199.

Barbour health and safety microfilm, Barbour Microfilm Windsor.

Bioastronautics data book ed J F Parker and V R West NASA SP-3006National aeronautics and space administrationWashington DC.

Bittner A G Human Factors engineering principles for minimisingand Guignard J C adverse ship motion effects: theory and practice.

Naval Engineering Journal 97(4) pp 205-213.

Broadbent D E Effects of noise on behaviour. In; C M Harris (ed)Handbook of noise control (second edition)McGraw-Hill, New York.

Brown A Vawter F G and Temperature changes in human subjects duringMarberger J P exposure to lowered oxygen tension in a cool

environment. Journal of aviation medicine 23 pp456-463.

Bullard R W Effects of hypoxia on shivering in man. Aerospace,medicine 32 1143-1147.

Burgess B F The effect of hypoxia on tolerance to positiveacceleration Journal of aviation medicine 29 pp754-757 The effect of temperature on tolerance topositive acceleration Aerospace medicine 30 pp567-571.

A-2


Burns K C

Burns W

Clark N P,Taub,H Scherer, H F andTemple W E

Dean R D, McGlothlen,C L and Monroe J L

Fife I andMachine K A

Gauer O

Motion sickness incidence: distribution of time tofirst emesis and comparison of some complex motionconditions. Aviation space and environmentalmedicine 55(6) pp 521-527.

Physiological effects of noise. In: C M Harris(ed) Handbook of noise control. (Second edition)McGraw - Hill, New York.

Preliminary study of dial reading performanceduring sustained acceleration and vibrationAMRL-TR-65-11O Ohio.

Effects of combined heat and noise on humanperformance, physiology and subjective estimates ofcomfort and performance. Boeing Company TechnicalReport D2-90540, Seattle and Boeing CompanyTechnical Report 1964b) Performance andphysiological effects of CH-46A noise andvibration. Boeing Company Technical ReportD2-90583 Seattle.

Redgrave’s Health and Safety in FactoriesButterworths London.

The physiological effects of prolongedacceleration. German Aviation Medicine in WorldWar II, US Government printing office pp 579-580.

Glaister, D H Human response to +Gz ship-shock acceleration. RAFInstitute of Aviation Medicine Scientificmemorandum S109, Farnborough, Hants, and Humantolerance to impact acceleration (surgery 9:pp 191-198).

Greenleaf J E, Matter M,Effects of hypohydration on work performance andBosco J S, tolerance to +Gz acceleration in man. Aerospace

Medicine 37 pp 34-39.

Grether W F Effects of combined heat, noise and vibrationstress on human performance and physiologicalfunctions. Aerospace Medicine 42 1092-1097 andFurther study of combined heat, noise and vibrationstress. Aerospace Medicine 43 pp 641-645.

Griffin M J et al Vibration and display perception, section 4.1. inengineering data compendium: Human perception andperformance. Edited by Boff K R Lincoln J E andWright-Patterson A F B Ohio: Armstrong AerospaceMedical Research Laboratory.

Guide to the Chemical hardening of equipment. CDE. Technical memo 79

Hale H B Human cardio accelerative responses to hypoxia incombination with heat. Aerospace Medicine 31, pp276-287.

A-3


Harris C S andSommer H C

Health andSafety Executive.

Hockey R andHamilton P

Kemp K H andWetherell A

King R andMagid J

Lloyd ARJM

Harris C S and Combined effects of noise and vibration onShoenberger, R W psychomotor performance. Aerospace medical

reserarch laboratory report AMRL-TR-70-14 NTIS noAD-710595. Combined effects of broadband noise andcomplex waveform vibration on cognitive performanceand response time. Aviation space andenvironmental medicine 51, pp 1-5

Interactive effects of intense noise and low-levelvibration on tracking performance and responsetime. Aerospace medicine 44, pp 1013-1016.

Publications catalogue, published annually,Guidance note EH40 Occupational exposure limits,published annually and regulations for control ofsubstances hazardous to health (COSHH).

The cognitive patterning of stress states. Stressand fatigue in Human Performance (ed Hockey R),Wiley.

Some effects of wearing impermeable gloves,protective, NBC, on manual dexterity. CDE TN 286,A laboratory study of the performance of men takingpyridostigmine bromide orally (30 mg eight hourly)for two weeks (1981) CDE TN 494 and some effects ofintramuscular injections of 2 mg atropine sulphateand 5 mg diazepam on human cognitive andpsychomotor performance CDE TN 532.

Industrial hazard and safety handbook Butterworths,London.

Ship motions, wind and the helicopter. Symposiumon Helicopters and the marine environment. RoyalAeronautical Society.

Loeb M A preliminary investigation of the effects of wholebody vibration and noise AMRL report no 145.

Malcolm R Pilot disorientation and the use of a peripheralvision display. Aviation, Space and EnvironmentalMedicine 55 pp 231-233.

Martin E E, and The effects of time and temperature upon toleranceHenry, J P

McCauley MWylie C D,and Mackie

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E, Royal J W,Motion sickness incidence: Exploratory studies ofO’Hanlon J F habitation, pitch and roll and the refinement of aR R mathematical model. (Technical report no 17333-2)

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A-4


McLeod, R W and A design guide for visual display and manual tasksGriffen H J in vibration environments. Part II "ISVR"

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Murakami S and Deguchi K New criteria for wind effects on(1981) Murray and pedestrians. Journal of wind engineering andMcCally industrial Aerodynamics.

North Atlantic Treaty Defence Research Group, Panel 8 (Human Factors)Organization (NATO)

Nicogossian A E andParker J F Space

Pheasant S

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Aviation psychology Ames Iowa State UniversityPress 270-276

The effect of a long duration exposure to noise andvibration on task performance. University ofLondon Msc thesis.

Some effects of a combined noise and vibrationenvironment on a mental arithmetic task. Journalof sound and vibration 95(2) pp 203-212.

Smith D E

Sommer H C andHarris C S

"A statistical examination of three approaches forpredicting motion sickness incidence". Aviation,Space and En.

Combined effects of noise and vibration on humantracking performance and response time. Aerospacemedicine 44 pp 276-280.

Space transportation system payload safety guidelines handbook JSC 11123Houston, Tx: LB Johnson space centre.

Stoddart C (ed) "Health and Safety case law index". KluverPublishing Ltd London.

Stokes J W System requirements for weightless environments.MSFC-STO-512A Huntsville Ala" G C Marshall spaceflight centre.

Strong R J Improving Warship Operability Limits: the effectsof ship motion on personnel. Institute of NavalMedicine working Paper. INM, Gosport, Hants March.

A-5

INT DEF STAN 00-25 (PART 5)/1ANNEX A (Concluded)

Taliaferro E H, The effects of minimal dehydration upon humanWempen R R and tolerance to positive acceleration, AerospaceWhite W J Medicine 36 pp 922-926.

Threshold Limit values and biological exposure indices (TLV’S) Publishedannually.

Viteles M S and An experimental investigation of the effect ofSmith K R change in atmospheric condition and noise upon

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Vykukal H C Dynamic response of the human body to vibrationwhen combined with various magnitudes of linearacceleration. Aerospace Medicine 39. pp 1163-1166.

WHO Non-ionising radiation protection (ed) M Suess.

WHO Regional Publications Euroseries No 10 Copenhagen.

A-6

INT DEF STAN 00-25 (PART 5)/1ANNEX B

Sources of Advice

B.1 The Submarine Atmosphere

B.1.l Sea Systems Controllerate.Chief Naval ArchitectSubmarine Safety Section NA 113FoxhillBath

B.1.2 The Institute of Naval Medicine(Senior Medical Officer, Submarines (SMO(SM))AlverstokeP012 2DL

B.2 Whole Body Motion Phenomenon

B.2.1 Army Personnel Research Establishment (APRE) Farnborough HantsGU14 6TD.

B.2.2 Institute of Aviation Medicine (IAM) RAE Farnborough.

B.2.3 Institute of Naval Medicine (INM) Alverstoke, Hants

B.2.4 Institute of Sound and Vibration Research, University ofSouthampton.

B.3 Vibration and Shock

B.3.1 Institute of Sound and Vibration Research (Dr M J Griffin). TheUniversity of Southampton, S09 5HN.

B.4 Weightlessness

B.4.1 European Space Research and Technology Centre (ESTEC). Noordwijk2200 AG, The Netherlands.

B.4.2 NASA G C Marshall Space Flight Centre, Huntsville, AL35812 USA.

B.4.3 NASA L B Johnson Space Centre, Houston, Texas 7705 USA.

B.5 Effects of Radiation

B.5.1 Army Radiation, Health and Safety Committee.

B.5.2 Naval Radio Hazards and Safety Committee.

B.5.3 RAF Radiation Health and Safety Committee.

B.5.4 Defence Radiological Protection Service c/o Institute of NavalMedicine, Gosport, Hants.

B.6 Chemical and Biological Contaminants

B.6.1 Chemical Defence Establishment, Porton Down, Salisbury, Wiltshire.

B-1

INT DEF STAN 00-25 (PART 5)/1ANNEX B (Contd)

B.6.2 Army Personnel Research Establishment Farnborough, Hampshire,GU14 6TD.

B.6.3 The Ergonomics Society c/o department of Human Sciences, Universityof Technology, Loughborough, Leicestershire.

B.6.4 Defence NBC Centre, Winterbourne Gunner, Salisbury, Wiltshire.

B.7 Safety Standards

B.7.1 Director of Safety Services, MOD(PE), Station Square House, St MaryCray, Orpington, Kent.

B.8 Combined Environmental Factors

B.8.1 APRE Farnborough, Hants

B.8.2 IAM Farnborough, Hants

B.8.3 INM Alverstoke, Hants.

B-2


c Crown Copyright 1992

Published by and obtainable from:Ministry of DefenceDirectorate of StandardizationKentigern House65 Brown StreetGLASGOW G2 8EX

Tel No: 041-224-2531/2

'This Standard may be fully reproducedexcept for sale purposes. Thefollowing conditions must be observed:

1 The Royal Coat of Arms and thepublishing imprint are to beomitted.

2 The following statement is to beinserted on the cover:‘Crown Copyright. Reprinted by(name of organization) with thepermission of Her Majesty’sStationery Office.’

Requests for commercial reproductionshould be addressed to MOD Stan 1,Kentigern House, 65 Brown Street,Glasgow G2 8EX

The following Defence Standard file reference relates to the work on thisStandard - D/D Stan 328/01/05.

Contract Requirements

When Defence Standards are incorporated into contracts users areresponsible for their correct application and for complying with contractrequirements.

Revision of Defence Standards

Defence Standards are revised when necessary by the issue either ofamendments or of revised editions. It is important that users of DefenceStandards should ascertain that they are in possession of the latestamendments or editions. Information on all Defence Standards is containedin Def Stan 00–00 (Part 3) section 4, Index of Standards for DefenceProcurement - Defence Standards Index published annually and supplementedperiodically by Standards in Defence News. Any person who, when making useof a Defence Standard encounters an inaccuracy or ambiguity is requested tonotify the Directorate of Standardization without delay in order that thematter may be investigated and appropriate action taken.

91/60026

DIRECTORATE OF STANDARDIZATION

MINISTRY OF DEFENCERoom 5131

Kentigern House 65 Brown Street Glasgow G2 8EX

Telephone: 041 248 7890 Ext 2526

Your reference

Our reference

328/01/05DateApril 1992

INTERIM DEFENCE STANDARD IMPROVEMENT PROPOSAL

Defence Standard No: 00-25 (Part 5) Issue 1

Title: Human Factors for Designers of EquipmentPart 5 Stresses and Hazards

The above Defence Standard has been published as an INTERIM Standard and isprovisional because it has not been agreed by all authorities concerned with itsuse. It shall be applied to obtain information and experience on its applicationwhich will then permit the submission of observations and comments from users.

The purpose of this form therefore is to solicit any beneficial and constructivecomment that will assist the author and/or committee to review the INTERIMStandard prior to it being converted to a normal Standard.

Comments are to be entered below and any additional pertinent data which may alsobe of use in improving the Standard should be attached to this form and returnedto the Directorate of Standardization at the above address. No acknowledgementwill normally be sent.

1. Has any part of the Standard created problems or required interpretationduring use:

❑ YES NO if 'yes' state,❑a. clause number/s and wording:

b. recommendation for correcting the deficiencies:

2. Comments on any requirement considered too rigid:

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